Buffalo Bills quarterback AJ McCarron (10) looks to throw during the first half of an NFL football preseason game against the Cleveland Browns, Friday, Aug. 17, 2018, in Cleveland. The Bills won 19-17. (AP Photo/David Richard)

ORCHARD PARK, N.Y. (AP) — The Buffalo Bills' offseason-long quarterback competition is down to two players now that AJ McCarron is seeking a second opinion to determine the severity of an injury to his throwing shoulder.

Coach Sean McDermott on Sunday declined to reveal many details on McCarron's status except to say the team is still evaluating the injury after initial tests were inconclusive.

And yet McDermott acknowledged the injury will have an immediate effect on McCarron's place in the quarterback pecking order with rookie first-round pick Josh Allen and returning backup Nathan Peterman still competing for the starting job.

"Look, any time you're not on the field it's not really an ideal situation in that regard," McDermott said. "If healthy, then we pick up where we left off."

Defensive tackle and team leader Kyle Williams is listed week to week after the 13-year veteran hurt his right knee early in the second quarter against the Browns.

While the Bills practiced outdoors, Williams was spotted by The Associated Press walking into the weight room. He walked without a noticeable limp but had a long black wrap covering most of his right leg.

Safety Micah Hyde's initial concerns on Friday turned to relief upon seeing Williams at the facility.

"That's Kyle. He's a tough guy," Hyde said. "You're going to have to cut that leg off for him not to be playing."

McDermott said rookie third-round pick Harrison Phillips will take over the starting job in Williams' absence.

Who starts at quarterback remains the major question with Buffalo preparing to host Cincinnati on Aug. 26.

With McDermott being cautious against rushing Allen's development, McCarron was considered the initial front-runner for the job. He is the most experienced quarterback on the roster after spending his first four NFL seasons as Andy Dalton's backup in Cincinnati before signing with the Bills in free agency in March.

McCarron struggled in his first preseason start and had little help from an offensive line that had difficulty stopping the Browns' pass rush.

He was sacked once, hit several times and finished going 3 of 6 for 12 yards during four series in which the Bills failed to generate a first down.

Allen replaced McCarron and led Buffalo on scoring drives — a touchdown and two field goals — on each of his three possessions. He finished 9 of 13 for 60 yards and showed poise by avoiding the pass rush and stepping up in the pocket to hit Rod Streater for a 2-yard touchdown pass in a third-and-goal situation.

He particularly cleaned up his inconsistencies after going 9 of 19 for 116 yards and a touchdown in overseeing the third-stringers during the entire second half of Buffalo's preseason-opening 28-23 loss to Carolina.

In calling Allen's performance a step in the right direction, McDermott isn't ready to hand the 22-year-old the starting job just yet.

"Let's just manage expectations," McDermott said. "He's a young player, and let's just take it one day at a time right now. A lot to be learned still."

Receiver Kelvin Benjamin is impressed by Allen's poise.

"I feel like he controlled the huddle," Benjamin said, before recalling a conversation he had with Allen.

"I asked him early on, like, 'Do you get nervous.' And he was like, 'No,'" Benjamin said. "I'm like, 'Man, you're better than me because my rookie year I was kind of nervous.'"

Peterman took the first snaps in practice Sunday during the portion open to reporters.

Peterman has put up the best numbers of the three. He's completed 17 of 20 attempts for 232 yards, with two touchdowns and interception.

He was selected in the fifth-round out of Pittsburgh last year and had a forgettable rookie season. McDermott's calculated gamble to bench Tyrod Taylor and start Peterman backfired after the rookie threw five interceptions in the first half of a 54-24 loss at the Los Angeles Chargers on Nov. 19.

NOTES: The Bills signed DT Tenny Palepoi, who was cut by the team before the start of training camp. He initially signed with Buffalo in March after spending three seasons with the Chargers. ... Backup P Cory Carter was waived/injured after he tore a knee ligament against Cleveland.